This application claims the priority of German patent Application No. 100 12 916.1 filed Mar. 16, 2000, which is incorporated herein by reference.
The invention relates to a protective apparatus for preventing the infiltration of contaminants in a fluid-operated percussion device, having a striking tool that is guided to move in a housing, and is driven by a percussion piston in the striking direction, and a seal that is supported at least indirectly on the housing, on the one hand, and on the striking tool, on the other hand, and has a securing portion that is fixedly disposed with respect to either the housing or the striking tool.
The publication DE 196 28 815 C1 discloses a protective apparatus of the general type mentioned at the outset. This apparatus shields the striking tool at its throughgoing opening from the housing that serves to support the striking tool against the outside environment, and thereby prevents the penetration of even small to dust-type contaminants into the region of the striking-tool guide.
Due to the extraordinarily-high stress on the striking tool, it must be heavily lubricated in the region of its guide, which typically comprises a plurality of guide portions that are spatially separated from one another in the longitudinal direction of the striking tool. Consequently, lubricants, in particular, infiltrate the region of the striking plane between the percussive piston and the striking surface of the striking tool facing the piston. With extended use, accumulation or deposits formed in this manner cause damage to the percussive piston and at least at the striking surface of the striking tool, thereby diminishing the effectiveness and economic viability of the entire percussion device.
It is the object of the invention to embody the general type protective apparatus mentioned above such that it prevents the infiltration of contaminants in the connection to the striking-tool guide in the direction of the percussive piston.
The object is accomplished according to the present invention by a percussion device having a protective apparatus for preventing the infiltration of contaminants, said device comprising: a fluid-operated percussion device, having a striking tool that is guided to move in a housing by a striking tool guide, and is driven by a percussion piston in the striking direction, and a seal that is supported at least indirectly on one of the housing and the striking tool and has a securing portion that is fixedly disposed with respect to one of the housing and the striking tool, with the seal being disposed between an inner guide portion of the striking-tool guide and a theoretical striking plane of the percussive piston on the striking tool, when seen in the direction opposite the striking direction, such that a countersurface on one of the striking tool and the housing tool, and which moves relative to the securing portion of the seal and is in contact with the seal, is unaffected by wear.
The basic concept of the invention is to arrange the seal between the inner guide portion, when seen in the opposite direction of the striking direction, of the striking-tool guide and the theoretical striking plane of the percussive piston against the striking tool such that the countersurface that moves relative to the securing segment of the seal and is in contact with the seal, is wear-free.
In other words, for the purpose of protecting the seal resting against the countersurface, over which the seal travels due to the back-and-forth movement of the striking tool inside the housing, against untimely damage, the countersurface is disposed in a region that sustains no damage, even with a conservative estimation of the anticipated, greatest-possible wear.
In view of the fact that the inner guide portion of the striking-tool guide facing the percussive piston must also be adequately lubricated, the seal is disposed such that it is effective behind the inner guide portion when seen in the direction opposite the striking direction. Hence, the infiltration of undesired contaminants from the region of the inner guide portion in the direction of the percussive piston can be extensively prevented, provided that the function of the seal is only impaired insignificantly, or not at all.
In a modification of the invention, the seal is disposed behind the inner guide portion and in front of a cushioning ring secured to the housing when seen in the direction opposite the striking direction, with the ring serving as a stop for limiting the motion clearance of the striking tool in the direction opposite the striking direction.
With this arrangement, the seal assumes a position between the inner guide portion (which faces the percussive piston) and the cushioning ring when seen in the axial direction of the striking tool.
As an alternative modification within the scope of the invention, the seal can also be displaced in the direction of the theoretical striking plane of the percussive piston.
In this type of embodiment, the seal is disposed between the theoretical striking plane of the percussive piston and a cushioning ring that is secured to the housing, when seen in the longitudinal direction of the striking tool, and serves as a stop for limiting the motion clearance of the striking tool in the direction opposite the striking direction, and lies behind the inner guide portion when seen in this direction.
In other words, the following sequence occurs in the aforementioned viewing direction: inner guide portion/cushioning ring/seal/theoretical striking plane of the percussive piston.
Accordingly, the cushioning ring additionally spaces the sealing region, in which the seal is effective, physically from the inner guide portion of the striking-tool guide.
The maintenance of the percussion device and the exchange of the seal can be simplified through the connection of the securing portion of the seal to an exchangeable receiving sleeve, which is in turn secured to the striking tool or a housing.
In the case of the latter variation, the receiving sleeve can also constitute a component of the cushioning ring, i.e., it can be combined with the ring to form a unit that is connected to the housing.
The protective apparatus is preferably embodied such that the motion clearance of the striking tool is shorter in the axial direction than the length of the countersurface on which the seal is supported. Consequently, even in extended operations, it can be ensured that the countersurface is not subjected to otherwise occurring wear, so the seal is protected against untimely damage.
Depending on the other circumstances, the seal can be embodied essentially as an inward directed or facing seal or as an outward directed or facing seal. Consequently, the securing portion of the seal is fixedly held relative to either the housing or the striking tool.
In the case of the embodiment as an inward directed seal, the countersurface over which the seal travels can be kept free from wear in that the diameter of the striking tool is smaller over the length of the countersurface than its diameter in the region of the inner guide portion. The difference in diameters should be in an order of magnitude that takes into account the anticipated wear in the region of the inner guide portion.
The discussed embodiment with an inward and/or outward directed seal can be further modified in that, in the installed state, the inside diameter of the inward directed seal is larger than the diameter of the striking surface of the striking tool that faces the percussive piston. Accordingly, the seal is widened when the striking tool is installed, so the seal rests in an elastic manner, and with prestressing, against the countersurface moving relative to the seal.
In an advantageous embodiment of the subject of the invention, the seal has at least one sealing lip that extends at an incline in the striking direction, and is kept in contact in an elastic manner against the countersurface.
It has proven advantageous to select the ratio of the length of each sealing lip to the greatest-possible transverse offset of the striking tool, relative to the housing, to be at least 1, preferably more than 1 to 3. Thus, it is ensured the seal also exerts an adequate sealing effect, even with the anticipated transverse movements of the striking tool inside the housing.